Causes and Consequences of Diachronous V‐Shaped Ridges in the North Atlantic Ocean

Abstract

In the North Atlantic Ocean, the geometry of diachronous V‐shaped features that straddle the Reykjanes Ridge is often attributed to thermal pulses which advect away from the center of the Iceland plume. Recently, two alternative hypotheses have been proposed: rift propagation and buoyant mantle upwelling. Here we evaluate these different proposals using basin‐wide geophysical and geochemical observations. The centerpiece of our analysis is a pair of seismic reflection profiles oriented parallel to flow lines that span the North Atlantic Ocean. V‐shaped ridges and troughs are mapped on both Neogene and Paleogene oceanic crust, enabling a detailed chronology of activity to be established for the last 50 million years. Estimates of the cumulative horizontal displacement across normal faults help to discriminate between brittle and magmatic modes of plate separation, suggesting that crustal architecture is sensitive to the changing planform of the plume. Water‐loaded residual depth measurements are used to estimate crustal thickness and to infer mantle potential temperature which varies by ±25°C on timescales of 3–8 Ma. This variation is consistent with the range of temperatures inferred from geochemical modeling of dredged basaltic rocks along the ridge axis itself, from changes in Neogene deep‐water circulation, and from the regional record of episodic Cenozoic magmatism. We conclude that radial propagation of transient thermal anomalies within an asthenospheric channel that is 150 ± 50 km thick best accounts for the available geophysical and geochemical observations.

Oceanic-like axial crustal high in the central Red Sea

“…In the Afar region, there have been pulses of volcanism (Audin et al, 2004;Barberi et al, 1975), so the variations in basement gradient in Figure 5d may have arisen from temporal changes in composition or temperature of the upwelling mantle. Others have remarked on the possibility of pulsating mantle plumes leaving V-shaped ridges south of Iceland and similar Vshaped ridges have been found elsewhere (e.g., Parnell-Turner et al, 2017;Vogt, 1971).…”

“…It includes an area south of the Azores, where a pair of ridges surrounding the Mid-Atlantic Ridge (MAR) form a giant V-shape in plan-view, believed to have resulted from a pulse of magmatism from the plume that has now ended, leaving the previous high rifted (Cannat et al, 1999;Escartin et al, 2001). The Reykjanes Ridge is surrounded by more than one V-shaped ridge, suggesting multiple pulses of magmatism (e.g., Parnell-Turner et al, 2017;Vogt, 1971). Ridges surrounding the Galapagos Spreading Centre have been interpreted as arising from magmatic pulses (Kappel and Ryan, 1986).…”

Fluid Circulation Along an Oceanic Detachment Fault: Insights From Fluid Inclusions in Silicified Brecciated Fault Rocks (Mid‐Atlantic Ridge at 13°20′N)

“…This OCC develops on the western flank of the MAR, which spreads at a full rate of 24.6 mm/yr (MacLeod et al., 2009; Smith et al., 2008) and is likely active based on its morphology, the absence of late tectonic disruption (Escartín et al., 2017; MacLeod et al., 2009; Mallows & Searle, 2012), and seismic activity. Microseismicity defines a curved fault plane reaching > 10 km below the ridge axis (Parnell‐Turner et al., 2017), reminiscent of that of other detachments such as Trans‐Atlantic Geotraverse (TAG) (deMartin et al., 2007) or Longqi (Tao et al., 2020). This OCC and its detachment fault were extensively investigated and sampled during the ODEMAR cruise, using deep‐sea vehicles (http://www.doi.org/10.17600/13030070).…”

“…Ridge sections hosting OCCs tend to be associated with high seismicity rates relative to magma‐rich, symmetrical ridge sections, and often display active hydrothermal venting (Escartín et al., 2008; Son et al., 2014). The microseismicity along the Northern Atlantic and the Southwest Indian Ridge detachments (deMartin et al., 2007; Parnell‐Turner et al., 2017; Tao et al., 2020) reaches sub‐Moho depths (between ∼8 and ∼13 km bsf). These results suggest that detachments are associated to a thick lithosphere, and that brittle deformation may provide potential pathways for fluid circulation reaching deep levels.…”

Observational estimates of dynamic topography through space and time

“…Lateral advection of an asthenospheric temperature anomaly from the proto-Icelandic plume beneath the basin is most compatible with these constraints (mechanism f in Figure 1; Rudge et al, 2008). Observations of V-shaped ridges of thickened crust down the Reykjanes oceanic spreading centre provide independent support for this Poiseuille-type flow within the Icelandic plume head (Vogt, 1971;Parnell-Turner et al, 2017).…”